Liquid containers are used as reagent liquid vessels in automated analyzers. When used in such an automated analyzer, reagent liquid is removed from the liquid containers by automatic pipettors. In modern systems this takes place in a rapid cycle in order to enable a high throughput of respective analytical processes. In this process the liquid container is rapidly conveyed to the pipetting station by means of a transport device e.g. in the form of a rotor and is braked there, whereupon the automatic pipette or suction needle dips into the withdrawal chimney through the upper opening of the liquid container in order to remove liquid by suction. In the case of automated analyzers with a high throughput only extremely short cycle times of a few seconds are available for each individual pipetting process including the positioning of the liquid container in the pipetting zone. The problem associated with this is that when the liquid container is abruptly stopped in the pipetting zone, the liquid in the container swashes and may spatter so that a reasonably equalized liquid level often does not occur until after a particular waiting time which takes longer than the required short pipetting cycle time for the high throughput operation. Usually pipetting should be avoided when the liquid level in the withdrawal chimney is still fluctuating because the pipette tip would be wetted on the outside with liquid over a relatively large area in an undesired manner and thus a relatively large entrainment volume of liquid would adhere to the outside of the pipette tip when the pipette is retracted from the liquid container and then cause contaminations in subsequent pipetting operations. In order to avoid this the pipette tip should also only slightly dip into the liquid to be pipetted during pipetting and the fill level in the liquid container should if possible be at rest. Also it should be avoided that the pipette draws air due to a fluctuating liquid level. Furthermore, foam formation in the withdrawal chimney should be suppressed. In the case of previously known liquid containers of the type under consideration here, this requirement can normally only be fulfilled within cycle times which would take too long for high throughput operation in automated analyzers.
Reference can for example be made to WO 97/12677 A1, to U.S. Pat. No. 5,102,631 or to DE 38 38 278 C1 with regard to reaction liquid containers of the prior art with a withdrawal chimney. In the liquid container from WO 97/12677 A1 the upper end of the tube-shaped withdrawal chimney is provided with a radially outwardly projecting flange with which it is supported in a hanging fashion on a spout of the container opening. The completely open lower end of the withdrawal chimney extends into the vicinity of the bottom of the liquid container so that liquid communication can take place through the lower opening of the withdrawal chimney between the withdrawal chimney and the surrounding inner space region of the liquid container. In order to allow the pressure between the inner space of the container and the environment to equalize during pipetting, slot-like reductions in the wall thickness are provided in the upper region of the withdrawal chimney which should enable air to flow in between the opening spout of the liquid container and the casing of the withdrawal chimney.
An embodiment example of a container from DE 38 38 278 C1 has a withdrawal chimney whose cross-section is substantially smaller than the cross-section of the upper container opening and this withdrawal chimney perforates a screw cap screwed onto the opening spout and is attached to this cap. A through-hole in the screw cap allows a pressure equalization between the inner space of the container and the outer environment. The withdrawal chimney reaches the vicinity of the container bottom so that liquid exchange can take place between the withdrawal chimney and the surrounding inner space of the container through the open underside of the withdrawal chimney. In a further embodiment example of DE 38 38 278 C1 the outer circumference of the upper end of the withdrawal chimney and the inner circumference of the spout surrounding the upper end of the withdrawal chimney are only slightly different so that no venting path of sufficient magnitude for pressure equalization between the interior of the container and the environment remains between the outer side of the withdrawal chimney and the inner surface of the spout. A through-bore in the casing of the withdrawal chimney is provided at its upper end for pressure equalization. The lower end of the withdrawal chimney is essentially completely open and spacer bars are provided at the lower end of the withdrawal chimney.
The liquid container known from U.S. Pat. No. 5,102,631 is constructed similarly to the last-mentioned embodiment example from DE 38 38 278 C1 and thus also has a through-hole in the casing of the withdrawal chimney at its upper end. The withdrawal chimney extends to the bottom of the liquid container but large lateral openings are provided in the casing of the withdrawal chimney at its lower end.
Experiments of the inventor on liquid containers of the prior art constructed as elucidated above have confirmed that when the container is rapidly positioned in a treatment zone, the liquid in the container swashes, splatters and may foam in the container and a calmed, equalized level does not occur in the withdrawal chimney until after a period that is not tolerable for high throughput analyzers.